The invention relates to a simplified valve apparatus and a method of making such a simplified valve apparatus.
There is a substantial need for relatively low cost valves which may perform a variety of functions in rather small and intricate apparatus. In many applications, such valves must be capable of operating with a high degree of precision, i.e., close at the proper time and open at the proper time. The medical field represents an area in which such valves have a high degree of utility.
One particular application is serum separator tubes which comprise tubular members having one end closed by a plug which is formed from an elastomeric material. Typically, the plug includes a one-way valve which is forced open as the serum separator tube is forced downwardly through a blood sample in a collection tube so as to allow the serum or plasma to flow into the separator tube. When the separator tube becomes stationary relative to the collection tube, i.e., just before contact with the formed elements of the blood, the one-way valve closes so as to isolate the plasma within the separator tube. The separator tube may then be withdrawn.
It has been found to be particularly desirable to utilize the separator tube in and of itself as the transport device for transporting the serum or plasma to the laboratory from the point at which the blood sample is taken. This requires that the one-way valve at the closed end of the separator tube be essentially leak-proof. My U.S. Pat. Nos. 3,661,265 and 3,799,342 disclose a substantially leak-proof valve which does permit the use of a separator tube as a transport device. The one-way valve disclosed therein essentially relies upon the elastomeric properties of the plug to return the valve to the closed condition, i.e., there is no force or bias acting on the valve when the separator tube is in the stationary position and the valve is closed. Rather the valve elements, when properly structured, merely contact one another when returning to a natural or unbiased state in which they were originally molded. Proper closure of these valves may be assisted by the tubular member if the inside diameter of the tubular member is slightly smaller than the outside diameter of the plug but the tolerances on the inside diameter of the tubular member are difficult to control particularly where the tubes are extruded.
U.S. Pat. No. 3,954,614 also discloses a valve and a separator tube which is characterized by little or no seating forces when the valve is in the closed position. The same is true with respect to U.S. Pat. No. 3,962,085 wherein the periphery of a disc acts on a valve which is closed when the disc is in the closed position. However, there are no substantial seating forces beyond the weight of the blood sample itself. Valves such as those shown in U.S. Pat. Nos. 1,777,408 and 2,191,636 are biased so as to provide a substantial sealing force when in the closed position, but such valves are relatively complex.